The effects of internal and external cooling when exercising in heat

Exercising in extreme heat increases body temperature, having a detrimental effect on sporting performance as well as severe health consequences, evidenced during the Australian Tennis Open in 2014. Precooling techniques and interventions ameliorate exertion heat stress and mediate the decline in sporting performance. Precooling can be internal or external but no evidence has compared the approaches.

The vast number of cooling techniques reflects the challenge of providing a large cooling impulse through a technique that remains practical for use across a number of venues. Considerable growing evidence supports the use of internal cooling through ice slurry ingestion. From an exogenous perspective, mixed-method whole-body external cooling is gaining prominence following the apparent limited effectiveness of individual cooling garments on endurance performance.

Project aims

The aim of this study was to compare the physiological responses with practical and evidenced internal and external precooling techniques through the markers of lactate thresholds.

Our first hypothesis stated both precooling techniques would increase lactate threshold, improve running economy (RE), and increase maximum oxygen uptake, relative to no cooling. These variables are established markers of endurance performance that are known to be impaired under heat stress. Our second hypothesis stated internal cooling would elicit the greatest improvement within these markers because of the magnitude of core temperature reduction, and the size of effects previously reported for this technique.

Twelve males completed three incremental, discontinuous treadmill tests in the heat with core temperature monitored throughout. The trials were preceded by 20 minutes of either:

Internal cooling - Ice slurry ingestion
External cooling - Ice packs to quadriceps, ice vest, hand and forearm immersion in 9ºC water and frozen towels on head and neck.
No intervention

Project findings and impact

The aims of this study were to compare the physiological responses from internal and external precooling methods during graded exercise tests in the heat.

In accordance with our first hypothesis, both precooling interventions resulted in greater predicted running speeds at fixed blood lactate of 2 and 3.5 mmol/L compared with no cooling. However, no difference in RE or increase in maximum oxygen uptake was observed.

Prior to exercise, internal precooling had the greatest effect lowering T_CORE. Despite a failure to initially lower T_CORE, external cooling demonstrated a meaningful mediation of the rise in T_COREduring exercise. This different thermoregulatory response, suggests specific event characteristics will determine the choice of cooling.

Research team

Dr Neil Maxwell

Dr Alan Richardson

Dr Peter Watt

Oliver Gibson

Carl James

Output

Research project poster (pdf)

Journal of Thermal Biology report (pdf)

New York Times article 27 May 2015

James, CA, Richardson, AJ, Watt, PW, Gibson, OR and Maxwell, NS (2015) Physiological responses to incremental exercise in the heat following internal and external precooling. Scandinavian Journal of Medicine and Science in Sports 25 (S1) 190-199.

James, CA, Richardson, AJ, Watt, PW and Maxwell, NS (2014) Reliability and validity of skin temperature measurement by telemetry thermistors and a thermal camera during exercise in the heat. Journal of Thermal Biology 45 (October) 141–149.

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